In the past (2011) I had a wallet with address: 182TnmtTAStyMyBgAMBrRKNbtC1JqgC6HpI bought 1 BTC and spent it. Nothing strange here.Then I bought 4 BTC and did nothing with it.Then after some months (in the beginning of 2013) I saw that the 4 BTC were transferred without my knowledge.

Maybe somebody here can explain this?Are they stolen somehow or transferred to another address within my wallet?At that time I had a offline wallet (wallet.dat) on my computer which I still posses on a USB stick.

This is the transaction id: 8c11f74362e52c563089125516fabe82907d8469c49d34edc5f8eaaa88eb445a

In the past (2011) I had a wallet with address: 182TnmtTAStyMyBgAMBrRKNbtC1JqgC6HpI bought 1 BTC and spent it. Nothing strange here.Then I bought 4 BTC and did nothing with it.Then after some months (in the beginning of 2013) I saw that the 4 BTC were transferred without my knowledge.

Maybe somebody here can explain this?Are they stolen somehow or transferred to another address within my wallet?At that time I had a offline wallet (wallet.dat) on my computer which I still posses on a USB stick.

This is the transaction id: 8c11f74362e52c563089125516fabe82907d8469c49d34edc5f8eaaa88eb445a

It doesn't look like it has been transferred to an adress of your wallet, but rather some kind of mixing service / 3rd party, due to the long chain of transactions that follows. I'd say it is more likely that the funds were stolen.

Did you create the wallet.dat yourself or did you use a thirdparty to create the privkeys for them? That could be the reason, other then that, i couldn't imagine how your BTC got lost.

In the past (2011) I had a wallet with address: 182TnmtTAStyMyBgAMBrRKNbtC1JqgC6HpI bought 1 BTC and spent it. Nothing strange here.Then I bought 4 BTC and did nothing with it.Then after some months (in the beginning of 2013) I saw that the 4 BTC were transferred without my knowledge.

Maybe somebody here can explain this?Are they stolen somehow or transferred to another address within my wallet?At that time I had a offline wallet (wallet.dat) on my computer which I still posses on a USB stick.

This is the transaction id: 8c11f74362e52c563089125516fabe82907d8469c49d34edc5f8eaaa88eb445a

It doesn't look like it has been transfered to an adress of your walet, but rather some kind of mixing service / 3rd party, due to the long chain of transactions that follows. I'd say it is more likely that the funds were stolen.

Did you create the wallet.dat yourself or did you use a thirdparty to create the privkeys for them? That could be the reason, other then that, i couldn't imagine how your BTC got lost.

I did create the wallet myself but what I remember it was without a password, that option came later.

I think is stolen, mixing service can be used if you want to spend your bitcoins on the darknet in the marketplace. For me, it looks like your PC had malware/virus or remote control software. I think somebody once gained access to your PC was searching for *wallet*.dat and that file was stolen from you. Why do I think this way?If you didn't create this transaction and whole 4 BTC has transferred this points you been hacked and someone was waiting to make that transfer and you didn't set password that could slow down process but it will not stop from stealing, I've seen on Internet *offers* to crack password protected wallet.dat files is someone lost password.

I can only advise you in future to consider hardware wallet like Trezor or Ledger Nano S purchased from an authorised dealer or better from the manufacturer. Never keep all your crypto in one wallet, anything above 0.3 BTC store in cold storage. I use Veracrypt Encryption software, and online PC have wallet addresses but no private keys.Two separate containers above 1GB files - take some time to copy, and in cold storage private keys and passwords, but once I have 0.5 BTC I will buy hardware wallet.